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In the power grid, various conditions may occur that saturate the core of a current transformer. Saturation of the protection core of the current transformers can cause a malfunction in the protection relays. To prevent malfunction of the protection relays caused by the current transformer saturation, software and hardware methods can be used. In the software method changes in the protection relay algorithm are used. In the hardware method special devices are used. A new hardware method is presented here, which uses compensation to prevent the occurrence of current transformer saturation. In the proposed method, compensation is done by controlling an applied voltage to the current transformer secondary terminals using negative resistance. The proposed method, despite its simplicity and cost‐effectiveness, has good performance in preventing saturation in various conditions. The high reliability in terms of the risk of secondary open circuit and its application in various saturation conditions, even in the case of severe saturation are the main advantages of the proposed method. Also, the proposed method does not produce distortion in the transformation of high‐order harmonics by the current transformer. To verify the effectiveness of the proposed method, prototype design and construction have been performed. The simulation and experimental results of laboratory tests have been presented and analysed. [ABSTRACT FROM AUTHOR]

The magnetic effects and consequently the radial force are the main causes of noise in switched reluctance motors (SRMs). In this study a new design for SRM is developed in order to reduce acoustic noise. In this research a new design for SRM is developed in order to reduce the acoustic noise. In this investigation, at first, different SRM structures are simulated using JMAG software. An 8/6‐pole SRM is designed and built with special modification in the rotor and stator structures. For increasing mechanical strength, trapezoidal stator and rotor pole shape with poles arc βr = βs = 21° are proposed. In this design the taper angles of stator and rotor poles are equal. For noise reduction, the mechanical restructuring is done according to stress analysis. The new designed SRM are simulated and tested experimentally under no‐load and full‐load conditions. The results are shown and compared. Comparison between these results and the results of other structures shows that the acoustic noise of the newly designed motor is reduced considerably. The results show an acoustic noise reduction of ∼72% in new structure SRM. [ABSTRACT FROM AUTHOR]

This study proposes an adaptive sliding mode type‐2 neuro‐fuzzy control scheme for power‐control and speed‐control modes of doubly fed induction generator (DFIG). DFIG‐based wind turbine system operates as variable‐speed wind energy conversion system (WECS) with constant frequency. In the proposed controller design, a sliding mode control (SMC) strategy is used for online training of the parameters of type‐2 fuzzy set (T2FS) membership functions. Due to the uncertainty of the wind speed and variation in parameters in the WECS, an interval T2FS is used in the proposed control scheme. Based on the controller inputs, the SMC adaptive strategy is used to tune the parameters of antecedent and consequent parts of T2FS. These inputs are active and reactive power and rotor speed errors and their time derivative. These inputs fed to the type‐2 neuro‐fuzzy system. The results of simulation for a 1.5 MW DFIG‐based WECS are compared with the classical proportional–integral (PI) controller and type‐1 neuro‐fuzzy controller to validate the effectiveness of the proposed controller in power‐control and speed‐control regions. The results of simulation indicate that, in comparison to the PI and type‐1 neuro‐fuzzy controller, the proposed control scheme has better performance in both power‐control and speed‐control modes. [ABSTRACT FROM AUTHOR]

An essential requirement to improve the lightning performance of transmission line is the achievement of low impulse impedance of grounding system, which diminishes the occurrence of the external overvoltages. In this study, for the first time, a multi‐cross structure used as transmission line tower‐footing grounding system is investigated by means of hybrid continuous circuit‐trapezoidal integration method (HCCTIM). It is discovered that the angle of minimum impulse impedance or the optimal structure of multi‐cross grounding system is mainly dependent on the branch length compared to the effective length of a single horizontal conductor. Furthermore, in the current work, the trapezoidal integration method is used to solve the continuous circuit equations which elements are extracted from electromagnetic integral method, called HCCTIM. Coupling elements and soil ionisation are considered in this model. This method is an accurate, simple, and less time‐consuming computational method. The comparison of the results with measurements, other recent simulations and CDEGS software, satisfactorily validate the proposed method. [ABSTRACT FROM AUTHOR]

This study presents an adaptive sliding mode type‐2 neuro‐fuzzy controller for power control of doubly fed induction generators (DFIGs). DFIG‐based wind turbine system is variable‐speed constant‐frequency wind energy conversion system. In this proposed control scheme, in order to enhance its performance, sliding mode control (SMC) theory is used for online training the parameters of type‐2 fuzzy system membership functions. To regulate the antecedent and consequent part parameters, the SMC adaptive technique is used according to the controller inputs. These inputs are active and reactive power errors and their time derivative, which applied to the structure of T2NF system. The proposed controller employs an interval type‐2 fuzzy system because of the uncertainties of the wind speed and variation in parameters in the wind power conversion system. The simulations carried out for a DFIG‐based 1.5 MW wind turbine. The results of simulation are compared with the classical proportional–integral controller to confirm the effectiveness of this control scheme. This comparison is carried out between the cut‐in and rated region wind speeds. The results of simulation show that the proposed control scheme has better performance to track the peak power and is more robust to machine parameter variations. [ABSTRACT FROM AUTHOR]

The loss of excitation (LOE) is one of the main faults of the synchronous generator, which may cause serious damages to generator and makes the power system unstable. The main problem to distinguish between LOE and stable power swing (SPS) is a time delay, which is a main part of the detection time in all recent protection methods. This study presents a new method for LOE detection in the synchronous generator, which reduces time delay by half. The proposed method exploits a new index which is based on the variation of the generator output reactive power. It is a combination of the first- and secondorder derivative of the generator output reactive power. In this method, after the generator losses its excitation, the proposed index will become and remain negative for a while. To prevent mal-operating under slowest power swing condition, the time delay of 0.85 s is used. The performance of the proposed method is evaluated under different conditions. The simulation results and experimental tests confirm the accuracy and fast operation of the proposed method. [ABSTRACT FROM AUTHOR]

Here, based on wide‐area measurement systems (WAMS), an adaptive tripping index (TI) is proposed for online prediction of tripping signals with respect to wide‐area out‐of‐step (WAOOS) protection of synchronous generators. The proposed TI included two different equations consisting of a straight line for unstable inter‐area oscillations and a sinusoidal line for WAOOS transient instability. For online identification of coherent generators with respect to inter‐area oscillations, based on evaluating the correlation coefficients between generator behaviours, an index is proposed from which the global tripping signals (GTS) are calculated. The GTS consist of the rate of change of inter‐area rotor angle oscillation between two oscillating areas in the centre of inertia frame. Actually, the proposed scheme is an adaptive and online index from which the critical inter‐area angle is adjusted individually by evaluating GTS at each sampling time gathered from the WAMS data. The proposed strategy is implemented on an IEEE 39‐bus test system and its performance is investigated by simulating typical scenarios during time‐domain simulations. The results show the effectiveness of the proposed scheme for fast prediction of WAOOS protection in real‐time environment. [ABSTRACT FROM AUTHOR]

In engineering terms, it is always desirable to maximise the efficiency of the motor and to look the problem in economic viewpoint, minimisation of the weight and cost of the motor is required. As these two aspects are like two sides of a coin, it is usually aimed to acquire the best efficiency per weight and cost. As a result, the performance improvement of permanent‐magnet synchronous motor (PMSM) has two sides: technical and economic. This study proposes a new approach for design optimisation of an interior PMSM (IPMSM) taking into account both technical performances and economic considerations. The selected rotor configuration is a good candidate for general purpose industrial applications. A multi‐objective optimisation technique based on a new and efficient magnetic equivalent circuit of the motor is applied to obtain optimal motor parameters. A Pareto front composed of possible optimal solutions is provided. The best optimal solution is then selected using a k‐means clustering algorithm. To verify the efficacy of the design optimisation, the performance characteristics of the optimal PMSM are compared by both the finite element simulations and the experiments. In the test setup, an 8‐pole, 200‐Watt, four‐phase IPMSM with an optimised structure is prototyped where the results give agreeable accuracy. [ABSTRACT FROM AUTHOR]

In conventional methods, distributing and chording the winding of a motor can be used for controlling the harmonic contents of magnetomotive force (MMF). This solution may not be able to reduce the harmonic contents of motors to the desirable value that may cause unsuitable performance of the motor such as crawling phenomenon. Moreover, the harmonic contents of the MMF cause increase of the losses and reduction in efficiency of electrical motors. The effect of the new winding scheme was investigated to improve the induction motor operation by reducing the harmonic contents of the MMF. By applying the new winding pattern in an induction motor, the harmonic component groups of fifth (5, 11, etc.) and seventh (7, 13, etc.) were reduced considerably. A simulation approach alongside experimental results derived from a two‐pole, 400 V, 50 Hz, 200 W, three‐phase induction motor validate the improvement operation of the motor. [ABSTRACT FROM AUTHOR]

Sinusoidal voltage waveform in synchronous generators is of great significance in power systems. Generally speaking, the output voltage of a synchronous generator is semi‐sinusoidal including some disturbance frequencies (known as harmonics) rather than the fundamental frequency. The harmonic contents cause them to increase in iron loss and reduction in efficiency of electrical machines. For this reason, the harmonic contents of synchronous generators should be carefully taken into consideration. In this study, a new winding pattern for stator of the synchronous generators is proposed to eliminate the harmonic contents of output voltage and so makes it more sinusoidal. In this method, the harmonic contents of output voltage are almost eliminated by selecting the optimal number of conductors per slot. Afterward, through several analytical and simulation studies the suggested winding pattern is compared with those of conventional ones. Moreover, the experimental setup is carried out based on a 3 kW, 1500 RPM synchronous generator. The conventional and proposed winding patterns are separately tested in this setup, and then the harmonic‐based behaviour of output voltage is studied for each case under different load conditions. The obtained results prove the superiority of the proposed winding pattern over the conventional patterns. [ABSTRACT FROM AUTHOR]

This paper presents a multiobjective optimal design of the parameters of surface‐mounted permanent magnet synchronous motors (PMSMs) considering saturation of the iron core. Multiobjective parameter tuning can further improve the performance characteristics of such motors. Specifically, efficiency and total volume are of great importance in industrial applications. A new formulation is presented for these two objective functions. In this paper, a multiobjective optimization based on a modified nondominated sorting genetic algorithm II (NSGA‐II) is utilized for optimal design of PMSM. Pareto‐optimal solution is achieved, and optimal variables are obtained. The best solutions are then selected by k‐means clustering algorithm for the motor under study. Finally, finite element analysis (FEA) is performed to validate the optimization procedure. The FEA results agree well with the values obtained by the optimization process. [ABSTRACT FROM AUTHOR]